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International audienceA measuring technique for antenna gain is presented, based on averaging a normalized transfer function over a distance range. Criteria for setting the distance range are drawn by investigating the effects of reflection and diffraction. Our method is compared to the time-gating method by measuring two low-gain, quasi nondirectional antennas

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Common mode currents on antenna feeders usually occur when feeding a symmetric radiator through an asymmetric line, or when the ground plane is electrically small. Such currents may have magnitudes comparable to the feed currents and therefore have a major impact on the total radiated field. For antenna radiation measurements, both assessment and reduction of the common mode currents on antenna feeders are crucial. Techniques to discriminate antenna and feeder radiation are mainly needed for design and optimization purposes. Antenna gain measurements in a multipath site can be performed by using the distance averaging method. In this paper, we show that the distance averaging technique can be applied to reduce the effect of common mode currents for measuring the field radiated by symmetrical antennas. Two measuring configurations are proposed depending on the number of symmetry degrees of the antenna under test, and a differential approach for extracting the field created by the common mode currents was also developed. The experimental validation was performed by measuring a simple wire dipole and a log-periodic dipole array (LPDA) with a small square loop as a probe, both on the feeder side and on the feeder free side.

This paper presents a characterization method for extracting the reflection coefficient of materials and the real part of their permittivity. The characterization is performed in a real environment, as opposed to the classical measurement methods that require an anechoic chamber. In order to reduce the effects of the multipath propagation, a free space bistatic measurement was performed at different distances Material-Antennas in far field. By using a Teflon sample and a commercial absorbing material sample, measurements have been performed in order to validate the characterization technique.

The measured IL of the miniature DBRs are 0.55 dB (parallel capacitors) and 0.44 dB (series capacitors), respectively. This leads to unloaded quality factors equal to 98 and 110, respectively. Hence, when the capacitors are connected in series a 12% improvement of unloaded quality factor of the miniature DBR can be obtained. The obtained %M are 76% (parallel) and 70% (series). The 6% difference is simply due to the meander realization used in the first case 0. CONCLUSIONSA new miniaturized DBR topology has been proposed. A capacitor connected in series with the stub allows reducing the miniature DBR size by 70%. Compared with the miniature DBR published in 0, the new topology leads to the same miniaturization ratio with improved performance, and more robust design. The obtained results are: an improvement of 12% for the unloaded quality factor and a better agreement between measurement and simulation results using the same CAD tool (ADS Momentum TM ). Based on the knowledge of the radiated far-field waveform for a given excitation, time-domain characteristic functions can be derived, allowing the evaluation of the antenna response for any other excitation waveform. Time-domain impulse response (or effective height) and time-domain reflection coefficient are such characteristic functions that provide a complete knowledge of the radiated field waveform and of the reflected voltage waveform at the antenna input, respectively; however, these functions of time are not essentially figures of merit. For this reason, energy-based descriptors have been derived from the above characteristic functions. Energy gain, energy pulse matching ratio, and normalized correlation coefficient are such descriptors.In a previous work [1], we proposed an energy reflection coefficient that can be calculated from the time-domain reflection coefficient. The latter was measured by using the time-domain reflectometry (TDR) technique. In this article, we propose a time-domain technique for measuring the impulse response of an ultra-wide band antenna. As opposed to traditional single-antenna techniques, our method can provide a simpler separation of the three signals at the antenna input (i.e., excitation signal, antenna input reflected signal, and received signal), even though they might be superposed. Measurements are performed in a low-noise environment, such as a Faraday cage; in that case, the antenna under test is placed close to one cage wall.Experimental results using our method are presented for a UWB folded dipole antenna operating in the lower band for military UWB applications.The time-domain differential single-antenna method provides accurate results as long as far-field conditions are granted. However, such a constraint prevents one from using the method to measure electrically large antennas. That is, the antenna under test cannot be placed too far away from the Faraday cage wall considered as a reflector, given that the shorter the distance, the longer the time-span available for extracting the response. It is obviously more d...

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